1. Field of the Invention
This invention relates to a split type internal combustion engine having its intake manifold divided into a first intake passage leading to its active cylinders and a second intake passage leading to its inactive cylinders and having therein a stop valve, the second intake passage being charged with exhaust gases during a split cylinder mode of operation.
2. Description of the Prior Art
It is generally known that internal combustion engines demonstrate higher fuel combustion and thus higher fuel economy when running under higher load conditions. In view of this fact, split type internal combustion engines have already been proposed as automotive vehicle engines or the like subject to frequent engine load variations. Such split type internal combustion engines include active cylinders which are always active and inactive cylinders which are inactive when the engine load is below a given value. The intake passage is divided into first and second branches, the first branch being associated with the active cylinders and the second branch associated with the inactive cylinders and provided with a stop valve. During low load conditions, the stop valve is closed to cut off the flow of air to the inactive cylinders so that the engine operates only on the active cylinders. This relatively increases active cylinder loads resulting in high fuel ecomony.
A split type internal combustion engine has been proposed which is associated with an exhaust gas recirculation system for re-introduction of a great amount of exhaust gases into the inactive cylinders to minimize inactive cylinder pumping losses during a split engine operation for much higher fuel economy.
One difficulty with such a split type internal combustion engine is the possibility of leakage of the re-introduced exhaust gases through the stop valve from the first intake passage branch into the second intake passage branch, resulting in unstable active cylinder operation during a split engine operation where a great pressure differential appears across the stop valve.
In order to prevent such exhaust gas leakage, it has been attempted to use a valve such as a poppet valve having high fluid sealability. However, this requires a large-sized valve drive means capable of providing a force large enough to drive the poppet valve. Another attempt has been made to introduce air, instead of exhaust gases, into the second intake passage branch to minimize inactive cylinder pumping losses during a split cylinder mode of operation. In this attempt, however, cold air is discharged from the inactive cylinders to the catalytic converter normally provided in the exhaust system to spoil its performance.
Such leakage of exhaust gases through the stop valve from the first intake passage branch into the second intake passage branch is mainly due to pressure waves resulting from exhaust pulsations and propagated through the EGR passage to the second intake passage branch to periodically increase the pressure differential across the stop valve between the first and second intake passage branches during a split cylinder mode of operation.